Shock wave generator

ABSTRACT

Apparatus for generating a shock front includes a fluidically actuated projectile-like valve member for rapidly opening and closing fluid passages between a reservoir within the valve member and a tube or pipe in which the shock wave is to be generated. Also, an improved fluid snap-valve is driven by a dual-surfaced piston having a high pressure on a smaller surface and a lower pressure on an oppositely-acting larger surface; increase of pressure on the larger surface snaps the piston to open the valve in a toggle-like fashion.

United States Patent Moffatt Jan. 16, 1973 [S4| SHOCK WAVE GENERATOR Primary ExaminerHenry T. Klinksiek An -M I P W'll' r [75] Inventor: E. Marston Moffatt, Glastonbury, army e earson 1 mm Com 57 ABSTRACT Assignefii United Aircraft Corporation, East Apparatus for generating a shock front includes a Hartford, Conflfluidically actuated projectile-like valve member for [22] Filed: 19, 1971 rapidly opening and closing fluid passages between a reservoir within the valve member and-a tube or pipe [21] Appl. No.: 190,502 in which the shock wave is to be generated. Also, an improved fluid snap-valve is driven by a dual-surfaced piston having a high pressure on a smaller surface and [52] US. Cl. ..251/29 a lower pressure on an oppositely acting larger sub [51] Int. Cl ..Fl6k 31/12 face; increase of pressure on the larger Surface Snaps 0 Search the piston to pen the valve in a toggle-like fashion [56] References Cited 4 Clalms, 12 Drawing Figures UNITED STATES PATENTS 3,514,07l 5/l970 Moffatt ..25l/3l g m5 #L-ffi 9 Z ZZ 7 XZ /flZ f yd 34/ i O00! l //Z W 9 n 5 L 56? 1 5 i i/zz j y 7 /i a PATENTEDJAHIBIBYS 711 061 swear 2 OF 3 SHOCK WAVE GENERATOR BACKGROUND OF THE INVENTION 1. Field oflnvention This invention relates to improved means for generating a shock front in a gas.

2. Description of the Prior Art In gas pipeline systems, it is known to utilize characteristics of the propagation of a shock wave or pressure pulse in the gas in the measurement of the flow of gas in the pipe. There are also other situations in which generation of a shock front in a gas is advantageous.

As described in U.S. Pat. No. 3,514,071 entitled SHOCK PULSE GENERATOR issued to the same inventor and assignee as this case, a shock front may be generated in a shock tube as a result of a pressure pulse moving therethrough. In the shock tube, the more highly compressed gas behind the pressure front catches up to and reinforces the leading edge of the pulse to create a shock front with a steep leading edge.

In the device disclosed in the aforementioned patent, a projectile type valve of a generally cylindrical nature having an annular array of holes therein provides momentary communication between a pressure tube connected to the pipeline in which a shock wave is to be generated and a chamber having a vastly different gas pressure than that of the shock tube. The projectiletype valve is impelled by fluid pressure acting on a double-area valve connected thereto through a push rod. Although the device of the type disclosed in said patent performs the shock front generation function adequately, it has been found desirable to improve on the reliability and durability of such devices. In addition,vto work at high pressures the device must be strong and to work at low pressures it must be very light.

SUMMARY OF THE INVENTION The object of the present invention is to provide improved shock wave generators and fluid snap valves.

According to the present invention, a hollow member forms a completely enclosed chamber except for an annular array of passages through the walls thereof, said member being impelled by fluid pressured past an annular inlet to a shock tube, the interior of said member being at a substantially different pressure than the pressure in said shock tube, whereby a pressure pulse is generated in said shock tube to form a shock front in the gas therein.

According to another aspect of the present invention, an improved fluid snap valve, a solenoid-actuated fluid snap valve is connected by a push rod to a piston which has a smaller area acted on by a high pressure and a larger area normally acted on by a low pressure, increasing the pressure on the larger area causing snap valve action to cause an extremely rapid opening of the valve.

In further accord with the present invention, the aforementioned snap valve is used to actuate the aforementioned shock wave generator.

A shock wave generator in accordance with the present invention is not only more rugged, durable and reliable, it is more easily machined than those known heretofore in the prior art. It therefore may operate in a self-lubricating fashion utilizing the gas in the system as a cushion between moving surfaces and as a cushion to arrest motion of the projectile-like valve member. The construction is readily adapted to simplification of machining operations which not only lower the cost but also enhance the overall quality of the product. The present invention provides an extremely light and strong device, capable of high speed operation over a wide range of pressure.

Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying draw- BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partially schematic, side elevation view of a shock wave generator operated by solenoid snap valves, in accordance with the present invention;

FIG. 2 is a sectional side elevation of a preferred embodiment of a shock wave generator in accordance with the present invention;

FIG. 3 is a partially sectioned elevation view of a forward section of the embodiment of FIG. 2;

FIG. 4 is a side elevation view of a central portion of the shock wave generator of FIG. 2, rotated slightly from the position shown in FIG. 2;

FIG. 5 is a top view of the central section illustrated in FIG. 4;

FIG. 6 is a top sectional view taken on the line 66 in FIG. 2;

FIG. 7 is a top elevation view ofa rear section of the embodiment of FIG. 2;

FIG. 8 is a partially sectioned elevation taken on the line 8-8 in FIG. 7;

FIG. 9 is a top sectioned view taken on'the line 9-9 in FIG. 2;

FIG. 10 is a side sectional view taken on the line 10-- 10 in FIG. 9;

FIG. 11 is a simplified sectioned illustration of-a solenoid snap valve in accordance with the invention as embodied to work with the shock wave generator of FIGS. 1-10; and

FIG. 12 is a simplified sectioned illustration of a solenoid snap valve, of the type shown in FIG. 11, in a more generalized form.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a shock wave generator in accordance with the present invention comprises a main body portion 20 which may suitably comprise a hollow cylindrical section 22 having a flange portion 24, a cap section 26 including accesses blocked by filler plugs 28, 30 and adapted to be threaded to a pipe 32 through which access is made to a pipeline or other area in which it is desired to generate a shock wave in a gas. The flange portion 24 is suitably secured such as by bolts or other means (not shown) to a pair of solenoid snap valves 34, 36 each of which has a respective pipe 38, 40 which may preferably be connected to the same pipeline or other area of gas under pressure as is the pipe 32, in a manner and for purposes which are set forth hereinafter.

Referring now to FIG. 2, the cap section 26 is seen to be threaded into the cylindrical section 22, and if desired, the joint 42 therebetween may be sealed with any suitable sealant such as that regularly sold in commerce under the name Permatex. The cap section 26 has an axial fluid passageway 43 therein to permit fluid communication between the shock wave generator and the pipe 32. The passageway 43 is counterbored at its downward end as seen in FIG. 2 so as to receive a forward section 44 which is described in more detail with respect to FIG. 3.The forward section 44 is generally of a hollow conical shape with a flange 46 extending therearound. The upper end has a step 48 therein to permit providing a seal with the cap section 26, such as by an O-ring 50 (FIG. 2). The forward section 44 has a small hole 52 therethrough to permit passage of a lubricant stored in a chamber 54 between the cap section 26 and the forward section 44 for lubricating a projectilelike valve, as is described hereinafter. The forward section 44 may be secured to an annular middle section 56 by suitable bolts 58 or by any other suitable means. The juncture between the forward section 44 and the middle section 56 may be provided with shims 60 to adjust the spacing of various portions of the device as is described more fully hereinafter.

The forward section 44 receives, in its inner conical surface, a hollowed-out central section 62 which is described in more detail in FIGS. 4 and 5. The central section 62 has a generally cylindrical portion 64, rounded bottom portion 66, and a conical upper portion 68. A number of fins 70-72 (which may conveniently be three or four fins) are disposed on the outer surface of the central section 62 and serve to space it from the forward section 44 and the middle section 56. The fins 70-72 are relatively wide and shallow along the cylindrical portion 64, and become progressively deeper and narrower toward the point of the conical portion 68. This permits sufficient room between the fins 70-72 for the rapid flow of sufficient fluid to create the desired pulse as described hereinafter. The fin 70 is provided with a passage 74 which abuts and communicates with the passage 52 in the forward section 44 to permit the flow of lubricant therethrough. As seen in FIG. 2, there is a generally cylindrical void providing part of a valve housing chamber 76 having a conical forward face 78 within the lower portion of thecentral section 62. This chamber is lined with a suitable lubricating material 80 such as porous bronze orother sponge material which may take the form of a cylinder bonded by a suitable cement to the cylindrical walls of the chamber 76. Lubricant which flows through the holes 54, 74 will be carried capillarily through the spongy material 80. As seen in FIG. 2, the lower portion of the middle section 56 is rounded in a fashion similar to the lower portion of the central section 62, but slightly larger, so as to provide an annular, dish-like fluid passageway 82 at the base of the central section 62.'The shims 60 described hereinbefore are provided to adjust the height of the passageway 82 by adjusting the relative spacing between the central section 62 and the middle section 56. The middle section 56 is bored centrally so as to provide an extension of the valve housing chamber 76 within the central section 62. The central section 62 is bonded, preferably by brazing, to the forward section 44 such that the fins 70-72 are firmly secured to the inner conical surface 84 of the forward section 44.

The middle section 56 has a deep annular groove 86 therein, leaving a thin cylindrical portion 56' (see FIG. 6) which has a plurality of radial passages 90 therethrough to permit fluid to flow from the annular slot 86 to the inside of the middle section 56. The inner bore of the middle section 56 has two additional cylinders of porous bronze 92, 94 cemented thereto so as to provide nearly continuous lubricated surfaces to ensure substantially friction-free sliding therein of the projectile-like hollow valve member 100. An annular space is formed between the hollow valve member 100 and the two cylinders of porous bronze 92, 94 when the hollow valve member 100 is in the position as shown in FIG. 2. The hollow valve member 100 has a plurality of radially extending passageways 101 disposed about the periphery thereof at a point so that the holes line up with the annular space 102. Thus, fluid in the annular slot 86 may pass through the passages 96 to the annular space 102 and through the passages 101 into the chamber formed within the hollow valve member 100. A longitudinal slot 104 is formed in one surface of the middle section 56 (at the left as shown on FIG. 2), having a radial passageway 106 extending therefrom which matches with a radial passageway 108 extending through the central section 62 into the chamber 76 within the middle section 56. The passageways 106, 108 are sealed in a suitable fashion such as by an O-ring l 10. The annular slot 86 is also connected by a longitudinal passageway 112 to a pipe 114 which in turn connects to a pipe 116 which communicates with the solenoid snap valve 34 (FIG. 1

The middle section 56 is closed off at its bottom end by a rear section 118, a top view of which is shown in FIG. 7, which comprises one wall of the valve housing chamber 76. The .rear section 118 has a hole 120 to receive the pipe 114, and an additional hole 122 to receive a similar pipe 122 therein. The rear section 1 18 has a boss 124 which aligns within the central bore of the middle section 56. Extending upwardly from the boss 124 is a cylindrical portion 126, which fits within a raised conical surface 127 in the bottom of the valve member 100, and comprises a walled duct extending into the chamber 76, closed off by a first portion of the lower end of the valve member 100. The rear section 1 18 has a bell shaped central opening 128 therethrough which is in the form of a nozzle, for a purpose to be described hereinafter. The boss 124 has an annular notch 129 (FIG. 8) to receive a suitable seal such as an O-ring 130 (FIG. 2).

Disposed about the cylindrical portion 126 of the rear section 118 is a valve stop section 132 which is shown in plan view in FIG. 9 and in section in FIG. 10, to which reference is had for further description. The stop section 132 is generally annular in shape, having a hole 134 in the bottom portion thereof, and a larger hole 136 in the upper portion thereof, which is in fluid communication with a second (radially outward) portion of the valve member 100. A plurality of radial passageways 138 extend from the larger hole 136 through the wall thereof. The large hole 136 provides an annular passageway between its walls and the outer walls of the cylindrical portion 126 of the rear section 118, which through the radial passageways 138, is in fluid communication with an annular void 140 formed within the central bore of the middle section 56 due to the absence of spongy bronze (80, 92, 94). This void 140 in turn is in fluid communication with a radially drilled hole 142 which may be plugged by a suitable plug 144. The radial hole 142 is in fluid communication with the pipe 122. Although not described in further detail, each end of the pipes l 14, 122; two points along the middle section 56; and an additional point on the forward section 44 are provided with annular slots for suitable seals such as O-rings of the type illustrated by the O-rings 50 and 130, referred to hereinbefore. Abutting against the rear section 118 is a thin welded spacing cylinder 146 against which a closure section 148 is disposed, being driven thereagainst by a threaded closure ring 150. Within the thin wall spacing cylinder 146 there is formed a void comprising a high pressure chamber 152. The pipe 122 is in fluid communieation with the snap valve 36 (FIG. 1) by means of a pipe 154 (FIG. 2).

The device may be assembled by first brazing the forward section 44 to the central section 62 as described hereinbefore. These combined sections 44 and 62 may then be secured through the middle section 56, (such as by the bolt 58) and the shims 60 adjusted until the passageway 82 is of the desired size. The cap section 26 is then threaded into the top of the cylindrical section 22, with a suitable seal at the threads, as may be desired.

Then the combined structure 44, 56, 62 is inserted into the cylindrical section 22 through the bottom. Thereafter, the valve 100 may be inserted, the valve stop portion 122 may be placed over the cylindrical portion 126 of the rear section 118 and these are inserted into the cylindrical section 22 through the bottom. Then the pipes 114, 122 are inserted into the rear section 118, and the spacer cylinder 146 is inserted. Thereafter the closure portion 148 is inserted and the closure ring 150 is screwed into place binding all of these parts into an integral unit. Thereafter the pipes 116, 154 may be threaded into the closure portion 148.

Operation of the shock wave generator of FIGS. l-I0 is described assuming that the device is connected to a source of high pressure gas by pipe 32 and both of the solenoid snap valves 34, 36 are closed (such that viewing the device as seen in FIG. 2, the pipes 116, 154 may be assumed to be sealed off). The high pressure in the pipe 32 passes through thepassageway 44 in the cap 26, in a plurality of voids formed between the fins 70-72, through the passage 82 and to the valve member 100. Because the valve member 100 is not extremely tight with respect to the spongy bronze material 80, fluid may leak to the chamber 76 about the valve member 100, through the passageways 108, 106 and 104 to the annular slot 106, through the holes 101, and into the middle of the valve member 100. The fluid also leaks from the annular slot 86 through the holes 92 in the annular void 102 along the lower edges of the valve member 100 and into the void 140 formed below the lowest piece of spongy bronze 94. This then pressurizes the hole 192 and all the passages in the valve stop section 132. Thus, all of the cavities in the device are at high, pipeline pressure at this time. With all the passages and chambers in the device at the same pressure, there is practically nothing except gravity holding the valve member 100 in the downward position; however, due to the longer length of bleed passageway to the bottom of the device, there may be slightly higher pressure at the top of the valve member than at its bottom.

To operate the device, both of the solenoid snap valves 34, 36 are opened at substantially the same time (some qualification is described hereinafter) so that the pipes 116 and 154 will the reach atmospheric pressure in only a few milliseconds. 'I he qualification is that the passages within the valve stop section 132 should be at an extremely low pressure prior to the time that the valve member 100 clears the cylindrical portion 126 of the rear section 118, so that there .will be a rapid jump in pressure on that portion of the bottom surface of the valve member 100 which normally rests against the stop section 132, so that snap action will occur. If the pressure within the stop section 132 is as high as that within the chamber 152, then only a linear acceleration will result. But if high pressure acts only on the surface 127 of the member 100 until it clears the cylindrical portion 126, and then acts on the entire bottom surface of the valve member 100 (four times as great an area) an extremely rapid snapping of the valve in the upper direction can occur.

With the pipes 116, and 154 vented to atmosphere, all of the chambers and passageways in the device with the exception of the passageway 82 and the chamber 152 rapidly drop in pressure towards atmospheric. When the pressure in the chamber 76 is about one quarter of the relatively high pressure in the chamber 152 (acting on roughly one quarter of the cross sectional area of the bottom of the valve member 100) the pressure differential will be sufficient to start the valve member 100 moving in an upward direction. After it travels a very small distance (such as one tenth of an inch) the entire bottom of the valve member 100 becomes subject to the pressure in the chamber 152 which quadruples the force and rapidly impels the valve member 100 upwardly. As the valve member 100 passes the passageway 82, the high pressure in the passageway 82 causes a rapid flow of gas through the holes 101 into the center'of the valve member 100'; when the holes 101 clear the passageway 82, the rapid blockage of the flow causes a very sharp shock wave to be generated to the passageway 82 which propagates outward to the passageway 44 and into the pipeline. When the valve member 100 passes the hole 108, it seals off the upper end of the chamber 76 forming a gaseous cushion so that the upper portion of the valve member 100 does not contact the conical surface 78, but rather compresses the gas, which arrests its motion and, due to the elasticity of the rapidly compressed gas, tends to return the valve member 100 to its bottom position as shown in FIG. 2. In addition, gravity acting on the mass of the valve 100 causes it to operate in a stable fashion, thus insuring a return in the lower position as shown in FIG. 2.

The valve member 100 will move sufficiently so that the full area at its base (rather than just the conical service 127) will be subjected to pressure within the chamber 152 in approximately I millisecond. In this span of time, it is true that the chamber 152 is being bled toward atmospheric pressure through the passageways in the stop section 132, the passageway 142 and the pipes 122 and 154. However, the pressure in the chamber 152 will only drop a few percent during this time, so substantially the full pipeline pressure is available to drive the member 100 rapidly upward as described hereinbefore. On the other hand, if the passages within the stop section 132 can be kept at low pressure (such as atmospheric) then the solenoid snap valve 36 could, be eliminated, as well as the passageways and pipes extending thereto from the stop section 132. For instance, the passages within the stop section 132 could be provided with a small bleed to atmosphere, so that pressure would never build up therein; however, this results in a loss of the gas in the system, which may, for instance, be natural gas having a value and creating a hazard. However, in a utilization of the invention wherein it may be suitably sealed off in the vicinity of the pipe 32 or the passage 44, so that the bleed would exist only when the device is in operation,

then such a bleed may indeed be appropriate. In any event, the snap valves 34, 36 and passageways connected thereto together comprise means for concurrently lowering the pressure within said hollow valve member and for rapidly actuating it.

Referring now to FIG. 11, one form of a-solenoid actuated snap-valve in accordance with the present invention is illustrated, in a configuration compatible with the shock wave generator of FIG. 1, described hereinbefore, as formed within a main housing structure 158.

A solenoid 160 mounted in a frame 161 comprises an electromagnet 162 and an armature 163, the armature being connected by a shaft 164 to a ball valve 165. The solenoid 160 is shown in the non operated position so that a spring 166 pushing on a disk 167 integrally formed on the shaft 164 forces the ball valve 165 upwardly to close a passageway 168 which is at a high pressure. As shown in FIG. 11, the passageway 168 communicates via a needle valve 170 and the pipe 38 with the gas pipeline in which a shock wave is to be generated (or with any other suitable high pressure source). With the ball valve 165 in the position shown, another passageway 172 is open to the atmosphere or other suitable low pressure source.

An assembly 173 disposed within a chamber 176 includes a main piston 174 provided with a sealing means 178 such as an O-ring. The piston is connected by a shaft 180 to a valve.l82 which seats against a generally conical surface 184 of a second chamber 186. The valve 182 has a minor piston 188 extending to the right thereof as seen in FIG. 11, which is disposed within an additional chamber 190. The minor piston 188 is provided with a suitable seal 192 such as an O-ring. The chamber 190 is in fluid communication with the pipe 38 by means of a passageway 194. The chamber 176 communicates through a passageway 196 to the pipe 116 which is connected (as seen in FIG. 2) to a number of the cavities within the shock wave generator 20. The chamber 186 is vented through a passageway I98 and a muffler 200 to atmosphere or other suitable low pressure. The dimensions of the minor piston 188 and the chambers 186 and 190 are chosen so that, as the cylinder assembly 173 moves from the position shown in FIG. 11 (with the valve 182 seated against the surface 184 so as to seal off the chamber 176) to the right as seen in FIG. 11, the minor piston 188 will abut a surface 202 in the chamber 190 and arrest the motion prior to the time that the main cylinder 174 will com mence to close off the passageway 176. In other words, when the valve assembly 173 is in its extreme rightmost position, the passage 196 will still open into the chamber 176.

Consider first conditions which obtain with high pressure at the pipes 38 and 116, and the ball valve 165 in the position shown. Since the area of the piston 174 is greater than the area of the valve 182, and since high pressure is acting on the right side of the piston 174 and atmospheric pressure is acting on the left side of the piston 174, together with the high pressure on the minor piston 188, there is a net force to the left as-seen in FIG. 11, and a seal is made. However, once the solenoid is actuated so that the ball valve shifts from the position shown to a position where it will block the passageway 172, then high pressure appears at the left surface of the piston 174. As soon as this pressure exceeds a balance (which will occur primarily because the area on the left face of the piston 174 is greater than the net area on the right face of the piston 174, and because atmospheric pressure is present in the chamber 186) the assembly 173 will begin to move to the right. However, as soon as the valve 182 opens with respect to the surface 184 by a very small amount, the right side of the chamber 176 immediately begins to bleed towards atmospheric pressure through the muffler 200. If there is a tight restriction in the line feeding the pipe 116 (which is true as described more fully hereinafter) the passageway 196 will not be able to replenish the gas as rapidly as it dumps through the valve 182 to atmospheric pressure. Thus, a very slight initial motion causes an extremely rapid loss of pressure in the right side of the chamber 176 which results in the assembly 173 rapidly snapping the rest of the way to the right as seen in FIG. 11, in a toggle fashion. The piston will thereafter remain in that position indefinitely untilthe solenoid 160 is again turned off.

It is well to note carefully at this point the lack of inconsistency in the operations being performed here. The initial motion of the assembly 173 (FIG. 11) is caused simply by an excess of pressure acting on the left side of the piston 174. If that were all that were to occur, the piston would move slowly to the right, opening the valve 182, and eventually bleeding the passageway 196 (and the many cavities of the shock wave generator, FIG. 2). However, snap action is achieved due to the fact that the passageway 196 cannot replenish the gas in the right end of the chamber 176 once the valve 182 opens a small amount, so the assembly 173 snaps to the right in FIG. 11. The fact that the restrictions prevent the passageway 196 from replenishing the gas in the chamber 176 does not preclude a rapid bleeding down of all the cavities connected thereto (FIG. 2), since this depends only upon the volume involved in the cavities within the shock wave generator and the flow volume permitted through the valve 182 after it has opened. Thus, although the flow of gas from FIG. 2 through the passageway 196 is sufficiently slow to permit snap action, once the device has snapped, a relatively unimpeded bleeding of the cavities through the passageway 196 will occur.

When the solenoid is deactivated, that portion of the chamber 176 to the left of the piston 174 again bleeds down to atmospheric very rapidly, so that both sides of the piston 174 and both sides of the valve 182 are at atmospheric pressure, being a rather neutral condition; however, high pressure appearing in the chamber 190 will act on the minor piston 192 and reset the device to the left, to the position as shown in FIG. 11. Once the valve 182 closes, the chamber 176 will again build up to the high pressure in the pipeline. 1

The pipe 116 which connects (P10. 2) to the shock wave generator 20 achieves the high pressure of the pipeline through the bleed down described hereinbefore, which occurs due to tolerances between the parts and the passageways described hereinbefore. Thus, over a period of time, the right side of the chamber 176 (FIG. 11) will achieve high pressure; however, once the valve 182 opens, the'constrictions in the shock wave generator (FIG. 2) between the pipeline and the pipe 116 are such that the gas cannot flow sufficiently to replenish the chamber 176 once it starts to dump to atmosphere. That is the essential feature of this aspect of the invention: a pressure differential starts the motion of the assembly 173, and this start bleeds the chamber 176 causing a great pressure differential across the piston 174 so that the assembly 173 then snaps to the right. In a similar fashion, the solenoid actuated snapvalve of this type has general utility if provided with a high pressure having a suitable restriction (so that the chamber 176 cannot be replenished) as shown in FIG. 12. In FIG. 12, if the pipe 116a were connected to a source of high pressure which is to be rapidly bled, but

does not itself provide the restriction as does the shock wave generator 20 herein, then a restriction 204 may be placed in the passageway 196a so as to provide the snap-like action described hereinbefore.

Both of the solenoids 34, 36 are of the type described with respect to FIG. 11. However, as described hereinbefore, it is important that the chambers and passages within the stop section 132 be bled down to a low pressure prior to the time that the valve member clears the cylindrical portion 126 of the closure section 118. This is achieved naturally if both operate simultaneously, due to the fact that there is less of a volume to be bled down within the passages of the stop section 132, the chamber 142, and the pipe 122, than there is in the entire remaining volume of the device which is in communication with the pipe 114. On the other hand, to enhance this and to ensure a very low pressure within the stop section 132 prior to the time that the valve member clears the cylindrical portion 126, the needle valve 170 in the snap valve 34 may be closed off more than the needle valve (similar to 170) in the snap valve 36, whereby the snap valve 36 will actually operate sooner than the snap valve 34.

Of course, the shock wave generator of FIGS. 2-10 may be operated with snap valves other than one of the type described with respect to FIG. 11 herein, so long as the selected valves will provide operation as described hereinbefore. Also, a single valve structure employing two assemblies 173 respectively venting two pipes 116, 154, actuated by one ball valve 165 could be utilized if desired.

Although the invention has been shown and described with respect to preferred embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes and 6 Having thus described typical embodiments of my invention, that which 1 claim as new and desire to secure by Letters Patent of the United States is:

1. A shock wave generator adapted to generate a pressure pulse in a high pressure gas comprising:

a pipe adapted for connection to gas under pressure in which the pressure pulse is to be generated;

a structure inconcluding a valve housing chamber and having a fluid passageway connected from said pipe to said valve housing chamber;

a hollow valve member disposed, when actuated, for motion within said chamber from a rest position therein to another position therein, said hollow valve member having fluid passages therein related to said fluid passageway within said structure so as to be in fluid communication therewith at a point along its path of motion; and

means for concurrently lowering the pressure within said hollow valve member and rapidly actuating said hollow valve member to move so that its fluid passages rapidly pass in fluid communication with said fluid passageway, whereby gas in said fluid passageway momentarily flows into said hollow valve member and then the flow thereof is rapidly arrested, thereby to generate a shock wave in the gas.

2. The shock wave generator according to claim 1 wherein said last-named means includes a fluid snap valve comprising:

a housing including a piston chamber;

a piston assembly including a piston disposed in said piston chamber and adapted for limited sliding motion within said piston chamber, said piston being slideably sealed against the walls of said piston chamber so as to provide two subchambers on either side thereof;

a low pressure outlet from a first one of said subchambers including a valve seat;

a valve closure member disposed on said assembly and adapted to seat against said valve seat and provide a closure of said first passage when said piston is in a first, rest position within said piston chamber, said valve closure member being opened in response to motion of said cylinder away from its rest position within its limited moving capacity;

means including a second passageway means in fluid communication with said first subchamber and with at least the fluid passages in said hollow valve member and said valve housing chamber when said hollow valve member is in its rest position, said means having the characteristic of being unable to replenish, with gas from said hollow valve member and said valve housing chamber, the gas in said first subchamber as it escapes through said valve and said low pressure passageway;

a third passageway, adapted for connection to a second source of gas at high pressure and a third source of gas at low pressure, and a rapidly-actuable operating valve therein alternatively connecting said second subchamber to said second source when said operating valve is in a first position and to said third source when said operating valve is in a second position; and

means for selectively placing said operating valve in said first position or said second position, alternatively.

3. A shock wave generator adapted to generate a pressure pulse in a high pressure gas comprising:

a pipe adapted for connection to gas under pressure in which a pressure pulse is to be generated;

a structure including a valve housing chamber having a longitudinal axis, one wall of said chamber having a walled duct extending into said valve housing chamber a distance equal to a small portion of the length of said valve housing chamber along its axis, said duct opening into said valved housing chamber;

a hollow valve member coaxially disposed within said valve housing chamber and adapted for motion along its axis between a first position, at which it is normally at rest with a first end thereof disposed against said walled duct and closing saidwalled duct off with a first end portion of said first end, and a second position, said first end being shaped to surround said walled duct when in said rest position and along a short axial distance therefrom, said hollow valve member having fluid passages extending through at least one wall thereof which is parallel with said axis, the dimensions of said hollow valve member, said valve housing chamber, and said walled duct permitting low flow volume leakage of gas at the pressure of the source around the outside surfaces of said hollow valve member;

first gas passageway means within said structure including passageways in fluid communication, when said valve member is in said rest position, when the fluid passages of said valve member and a forward portion of said valve housing chamber not occupied by said valve member;

second fluid passageway means within said structure and in fluid communication with that portion of gas passageway means, whereby the differential of fluid pressure in said high pressure chamber acting on said first end portion and the fluid in said forward portion of the valve housing chamber acting on a second end of said hollow valve member causes said hollow valve member to commence to move from its rest position, and for rapidly lowering the pressure in said second gas passageway means in a relation to the lowering of the pressure in said first gas passageway means to ensure that the pressure against said second end portion is signiflcantly lower than the pressure against said first end portion prior to the time that the motion of said hollow valve member causes it to cease blocking off said walled duct, whereby said hollow valve member is rapidly accelerated; and

a fluid passageway connecting said pipe with said valve housing chamber and disposed for fluid communication with the passages in said hollow valve member for a short distance substantially midway between its first and second positions. 4. A fluid snap valve comprising:

a housing including a piston chamber;

a piston assembly including a piston disposed in said piston chamber and adapted for limited sliding motion within said piston chamber, said piston being slideably sealed against the walls of said piston chamber so as to provide two subchambers on either side thereof;

a low pressure outlet from a first one of said subchambers including a valve seat;

a valve closure member disposed on said assembly and adapted to seat against said valve seat and provide a closure of said first passage when said piston is in a first, rest position within said piston chamber, said valve closure member being opened in response to motion of said cylinder away from its rest position within its limited moving capacity;

means including a second passageway adapted for connection with a first source of gas at high pressure which is to be rapidly bled by the snap valve and connecting said first subchamber with said first source, said means having the characteristic of being unable to replenish, with gas from said first source, the gas in said first subchamber as it escapes through said valve and said low pressure passageway;

a third passageway, adapted for connection to a second source of gas at high pressure and a third source of gas at low pressure, and a rapidly-actuable operating valve therein alternatively connecting said second subchamber to said second source when said operating valve is in a first position and to said third source when said operating valve is in a second position; and

means for selectively placing said operating valve in said first position or said second position, alternatively. 

1. A shock wave generator adapted to generate a pressure pulse in a high pressure gas comprising: a pipe adapted for connection to gas under pressure in which the pressure pulse is to be generated; a structure inconcluding a valve housing chamber and having a fluid passageway connected from said pipe to said valve housing chamber; a hollow valve member disposed, when actuated, for motion within said chamber from a rest position therein to another position therein, said hollow valve member having fluid passages therein related to said fluid passageway within said structure so as to be in fluid communication therewith at a point along its path of motion; and means for concurrently lowering the pressure within said hollow valve member and rapidly actuating said hollow valve member to move so that its flUid passages rapidly pass in fluid communication with said fluid passageway, whereby gas in said fluid passageway momentarily flows into said hollow valve member and then the flow thereof is rapidly arrested, thereby to generate a shock wave in the gas.
 2. The shock wave generator according to claim 1 wherein said last-named means includes a fluid snap valve comprising: a housing including a piston chamber; a piston assembly including a piston disposed in said piston chamber and adapted for limited sliding motion within said piston chamber, said piston being slideably sealed against the walls of said piston chamber so as to provide two subchambers on either side thereof; a low pressure outlet from a first one of said subchambers including a valve seat; a valve closure member disposed on said assembly and adapted to seat against said valve seat and provide a closure of said first passage when said piston is in a first, rest position within said piston chamber, said valve closure member being opened in response to motion of said cylinder away from its rest position within its limited moving capacity; means including a second passageway means in fluid communication with said first subchamber and with at least the fluid passages in said hollow valve member and said valve housing chamber when said hollow valve member is in its rest position, said means having the characteristic of being unable to replenish, with gas from said hollow valve member and said valve housing chamber, the gas in said first subchamber as it escapes through said valve and said low pressure passageway; a third passageway, adapted for connection to a second source of gas at high pressure and a third source of gas at low pressure, and a rapidly-actuable operating valve therein alternatively connecting said second subchamber to said second source when said operating valve is in a first position and to said third source when said operating valve is in a second position; and means for selectively placing said operating valve in said first position or said second position, alternatively.
 3. A shock wave generator adapted to generate a pressure pulse in a high pressure gas comprising: a pipe adapted for connection to gas under pressure in which a pressure pulse is to be generated; a structure including a valve housing chamber having a longitudinal axis, one wall of said chamber having a walled duct extending into said valve housing chamber a distance equal to a small portion of the length of said valve housing chamber along its axis, said duct opening into said valved housing chamber; a hollow valve member coaxially disposed within said valve housing chamber and adapted for motion along its axis between a first position, at which it is normally at rest with a first end thereof disposed against said walled duct and closing said walled duct off with a first end portion of said first end, and a second position, said first end being shaped to surround said walled duct when in said rest position and along a short axial distance therefrom, said hollow valve member having fluid passages extending through at least one wall thereof which is parallel with said axis, the dimensions of said hollow valve member, said valve housing chamber, and said walled duct permitting low flow volume leakage of gas at the pressure of the source around the outside surfaces of said hollow valve member; first gas passageway means within said structure including passageways in fluid communication, when said valve member is in said rest position, when the fluid passages of said valve member and a forward portion of said valve housing chamber not occupied by said valve member; second fluid passageway means within said structure and in fluid communication with that portion of said first end of said valve housing chamber external to said walled duct and thereby in fluid communication with a second end portion of said first end of said hollow valve member; a high pressure chamber within said structure and in high flow volume fluid communication with said walled duct and in low flow volume leakage fluid communication with said second area of said hollow valve member first end; means for rapidly lowering the pressure in said first gas passageway means, whereby the differential of fluid pressure in said high pressure chamber acting on said first end portion and the fluid in said forward portion of the valve housing chamber acting on a second end of said hollow valve member causes said hollow valve member to commence to move from its rest position, and for rapidly lowering the pressure in said second gas passageway means in a relation to the lowering of the pressure in said first gas passageway means to ensure that the pressure against said second end portion is significantly lower than the pressure against said first end portion prior to the time that the motion of said hollow valve member causes it to cease blocking off said walled duct, whereby said hollow valve member is rapidly accelerated; and a fluid passageway connecting said pipe with said valve housing chamber and disposed for fluid communication with the passages in said hollow valve member for a short distance substantially midway between its first and second positions.
 4. A fluid snap valve comprising: a housing including a piston chamber; a piston assembly including a piston disposed in said piston chamber and adapted for limited sliding motion within said piston chamber, said piston being slideably sealed against the walls of said piston chamber so as to provide two subchambers on either side thereof; a low pressure outlet from a first one of said subchambers including a valve seat; a valve closure member disposed on said assembly and adapted to seat against said valve seat and provide a closure of said first passage when said piston is in a first, rest position within said piston chamber, said valve closure member being opened in response to motion of said cylinder away from its rest position within its limited moving capacity; means including a second passageway adapted for connection with a first source of gas at high pressure which is to be rapidly bled by the snap valve and connecting said first subchamber with said first source, said means having the characteristic of being unable to replenish, with gas from said first source, the gas in said first subchamber as it escapes through said valve and said low pressure passageway; a third passageway, adapted for connection to a second source of gas at high pressure and a third source of gas at low pressure, and a rapidly-actuable operating valve therein alternatively connecting said second subchamber to said second source when said operating valve is in a first position and to said third source when said operating valve is in a second position; and means for selectively placing said operating valve in said first position or said second position, alternatively. 